<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var cup1 = '雪碧'
        var cup2 = '可乐'
        var cup3 = '';
        cup3 = cup1;
        cup1 = cup2;
        cup2 = cup3;
        console.log(cup1, cup2)
    </script>
</body>

</html>